ID: nht74-2.19

DATE: 10/22/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Truck Trailer Manufacturers Assoc.

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of September 4, 1974, in which you ask several questions regarding the possible manufacture of semitrailers designed to transport people. You state the semitrailers would be pulled by conventional tractors, would have air-operated bus-type side doors, a rear door for emergency exit, seats, handrails for passengers who stand, and windows that open and close. Communication between the passenger compartment and driver would be limited to a horn that the driver can blow and a blinking red light operable by either a passenger or the driver. You ask whether this type of vehicle is legal, whether it is legal to transport passengers in this fashion, and what specific requirements would be required to be built into the trailer.

We would consider the vehicles in question to be trailers under the Motor Vehicle Safety Standards, and consequently subject to the standards applicable to trailers. These standards are Standard No. 108, "Lamps, reflective devices, and associated equipment," Standard No. 106, "Brake hoses" (eff. as to trailers on September 1, 1975), and Standard No. 121, "Air brake systems" (eff. as to trailers on January 1, 1975), at this time. The trailers would, of course, have to be certified as conforming to all applicable standards, in accordance with the Certification Regulations (49 CFR Parts 567, 568).

Many States prohibit the transportation of passengers in trailers, and as a consequence NHTSA requirements for crashworthiness and occupant protection have not been made applicable to trailers. These requirements include those for restraint and seating systems, glazing materials, head restraints, and emergency exits. Whether or not State laws prohibiting the transportation of passengers in trailers would apply to semitrailers of this type would depend upon each State's interpretation of its law, and that information should be obtained from the various states. However, should it become a commonly permitted practice for persons to be transported in trailers, this agency would very likely expand its occupant protection and crashworthiness requirements through rulemaking to apply to these vehicles.

The transportation in interstate commerce of passengers for hire also falls within the regulatory authority of the Bureau of Motor Carrier Safety, in the Federal Highway Administration. We have forwarded your letter to that agency, requesting that it respond directly to you regarding the effect of regulations it administers on vehicles of this type.

Yours truly,

ATTACH.

Truck Trailer Manufacturers Association

September 4, 1974

James B. Gregory -- National Highway Traffic Safety Administration, Department of Transportation

Dear Dr. Gregory:

A member company is currently evaluating the possibility of manufacturing semitrailers which are detachable from the tractor, that are specifically designed to transport people or personnel. These trailers would be pulled over the Federal highways and would be pulled by a detachable conventional tractor. The trailers would be more or less conventional construction with the following basic specifications:

(1) The trailer would have an air operated bus type side door operated off the tractor air brake system.

(2) The trailer would have a rear door for emergency exit that could be operated from the inside.

(3) The trailer would be equipped with seats and handrails for those passengers standing up.

(4) The trailer would be equipped with windows that could be opened and closed.

(5) There would be no communication between the passenger compartment and driver compartment other than a horn that the driver can blow and a blinking red light that can be operated from either the interior of the trailer or the interior of the tractor.

Specifically, is this type of vehicle legal or is it legal to haul passengers over the highway with a detachable semitrailer of this type, and if it is legal what are the specific requirements that have to be built into the trailer?

We would appreciate receiving your thoughts on this matter.

Sincerely yours,

Burt Weller -- Engineering Manager

ID: nht74-2.2

DATE: 03/08/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Certain-Teed Products Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your January 25, 1974, question whether failure of a "common" clampband assembly on the "Camtite" emergency and parking spring brake, which would cause complete loss of air to the service brake system and failure of the emergency/parking brake portion of one unit, would be in violation of paragraph S5.7.2.2 of Standard 121.

The answer is no. S5.7.2.2 requires that failure of components common to the service and emergency braking systems shall not result in a loss of air that causes the parking brake to be inoperable. We interpret "parking brake" to mean the entire parking brake system. The failure you describe would not render the entire system inoperable, because all parking brakes other than the affected unit would remain operable.

This letter will be placed in the public file for the information of other interested persons.

Yours truly,

ATTACH.

CERTAIN-TEED PRODUCTS CORPORATION

January 25, 1974

Administrator -- National Highway Traffic Safety Administration, U. S. Department of Transportation

Re: Federal Motor Vehicle Safety Standard No. 121 - Air Brake Systems

Dear Sir:

We have been questioned by a customer for an interpretation as to the conformance of our CAMTITE emergency and parking spring brake design, as described in the attached brochure, to Paragraph S5.7.2.2., EMERGENCY BRAKING SYSTEM FAILURE, of FMVSS 121. This paragraph states:

"In the event of a failure of a valve, manifold, brake fluid housing, or brake chamber housing that is common to the service brake and emergency braking systems, loss of air shall not cause the parking brake system to be inoperable."

The service brake portion of our Camtite is "sectioned" in white and the emergency or parking spring brake portion in black on the Dimensional Drawing page of the enclosed brochure (SB-102). The clampband (Item #12 on the Parts List page) is common to both the service and emergency/parking brake portion of the unit.

We would appreciate a reply to the question: "Would failure of the "common" clampband assembly during a service brake application which could cause both loss of air and the complete "disengagement" of the service brake pressure side, as well as the total emergency/parking spring brake portion of the unit, be in violation of the intent of paragraph S5.7.2.2. of FMVSS 121?".

Very truly yours,

C. W. Mohr -- Vice President-Marketing

[Graphics omitted]

[Graphics omitted] REPLACEMENT PARTS NUMBER ITEM DESCRIPTION QTY. TYPE 24 TYPE 30 TYPE 36 1 Cylinder Assembly 1 47-31737-9 -- 47-40108-9 2 Piston Assembly 1 47-31797-9 -- 47-40093-9 3 Felt Wiper Ring 1 47-31805-9 -- -- 4 Piston Seal Ring 1 47-31799-9 -- -- 5 Seal Ring 1 36-524615 -- -- 6 Nylon Bushing 1 47-31745-9 -- -- 7 Bulkhead Seal Ring 1 47-31800-9 -- -- 8 Retaining Ring 1 47-31804-9 -- -- 9 Bulkhead 1 47-31747-9 47-31738-9 47-40095-9 10 Machine Screw 1 47-36161-9 -- -- 11 Follower 1 47-31785-9 -- -- 12 Clamp Band Assembly 1 40-31061-9 40-31062-9 40-31063-9 13 Self Tapping Screw 2 47-40012-9 -- -- 14 Diaphragm 1 40-31251-9 40-31165-9 40-31252-9 15 Return Spring 1 47-31258-9 -- -- 16 Non Pressure Plate 1 47-31364-9 47-31267-9 47-40098-9 17 Filter 1 47-31971-9 -- -- 18 Stop Washer 1 47-31974-9 -- -- 19 Snap Plug 1 47-31975-9 -- -- 20 Release Bolt 1 47-31970-9 - 47-40105-9 21 Capscrew 8 46-31656-9 -- -- 22 Spring (Light) 1 41-31920-9 -- -- Spring (Medium) 1 41-31921-9 -- -- Spring (Heavy) 1 41-31922-9 -- -- Spring (Booster) 1 47-40112-9 -- -40101 Push Rod (8.00 Proj.) 1 47-36034-9 47-31986-9 47-40102-9 Spring Locator 1 47-40191-9 -- --

NOTE: The symbol -*- indicates part is identical to part number listed in first column. Parts that differ are listed under appropriate type number. Parts shown are for complete units.

DIMENSIONAL DRAWING REFERENCES

A. AIR INLET ORIENTATION STANDARD 22 1/2 degrees +/- 3 degrees

B. CLAMP BAND ORIENTATION STANDARD 45 degrees +/- 3 degrees C. PUSH ROD PROJECTION (See back page)

D. YOKE CENTER PROJECTION (See back page)

CAMTITE

NOMINAL SPRING FORCES (OUTPUT OF COMPLETE UNIT)

[Graphics omitted]

CAMTITE

SPRING RELEASE PRESSURE NOMINAL RELEASE SPRING TYPE PRESSURE +/- 10% BOOSTER 30 LIGHT (40) 40 MEDIUM (50) 51 HEAVY (60) 62 MEDIUM PLUS 81 BOOSTER HEAVY PLUS 91 BOOSTER

NOTE: FOR EASE OF INSTALLATION ALL UNITS ARE SHIPPED IN MECHANICALLY RELEASED POSITION.

[Graphics omitted]

PUSH ROD AND YOKE SIZES

PUSH ROD PROJECTION:

Push Rod Projection is the Distance the Push Rod Extends Out from the Mounting Face of the CAMTITE Chamber. When Replacing Service Brakes with CAMTITE Chambers, the Push Rod Projection Length will Remain the Same. CAMTITE Standard Projection Length is 1-3/4" TYPE OF PROJECTIONS PART CHAMBER AVAILABLE NUMBER 24 1-3/4" (Std.) 47-31512-9 24 8" 47-36034-9 30 1-3/4" (Std.) 47-31511-9 30 8" 47-31986-9 36 1-3/4" (Std.) 47-40101-9 36 8" 47-40102-9

Other projections available upon special request.

(Illegible Word) ASSEMBLIES:

CAMTITE Yoke Assemblies are Available and may be Ordered as Complete Assemblies Containing Yoke, Yoke Pin, and Cotter Pin, or the Assembly Components May be Ordered Separately.

For Special Applications Requiring the Yoke to be Applied at Factory the Dimension from the Mounting Surface of the CAMTITE Chamber to Center Line of the Yoke Pin Should Be Specified.

[Graphics omitted] ASSEMBLY DIMENSIONS PART NUMBER 1 2 3 4 D 1-3/ 40360479 1-27/32" 1/2" 9/16" 8" 3" 1-3/ 40360489 1-3/4" 5/8" 9/16" 8" 3" 13/ 1-3/ 40360499 1-7/8" 3/4" 16" 8" 3"

**Figures for "O" Represent Standard Dimension Using Push Rods with 1-5/4" Projection.

ID: nht74-2.20

DATE: 05/13/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: American Trailers, Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your April 12, 1974, question whether a permanently attached steerable axle on a trailer is required (1) to meet the S5.3.2 stopping distance requirement with no uncontrolled lockup of any wheel above 10 mi/h, and (2) to meet the parking brake requirements for trailer converter dollies or for all other vehicles.

The answer to your first question is yes. The steerable axle(s) of any trailer must meet the stopping distance requirements of S5.3.2 with no uncontrolled lockup of wheels above 10 mi/h.

In answer to your second question, the permanently attached steerable axle you describe is not a separate vehicle which would qualify as a trailer converter dolly. Therefore the axle is simply part of a trailer which must meet the parking brake requirements of either S5.6.1 or S5.6.2. Neither of these options specifies that there be parking brakes on steerable axles, although in satisfaction of S5.6.2 (grade holding), the manufacturer could utilize parking brakes on the steerable axle.

Yours truly,

ATTACH.

April 12, 1974

James B. Gregory -- Administrator, National Highway Traffic Safety Administration

Dear Sir:

We manufacture a complete line of semi-trailers. Among these is a doubles grain trailer setup. In this doubles grain setup the lead trailer is a 24 foot, single axle semi-trailer which connects to the truck-tractor by means of a standard kingpin. The second trailer is a two axle, four wheel type of trailer, 21 foot long, which is connected to the lead trailer by means of a pintle hook-lunette eye attachment. The front axle on the second trailer is part of a dolly, which is steerable, and is permanently attached to the trailer by means of a bolted 360 degrees turntable.

Our question is one of interpretation. Is the front axle dolly a "converter dolly" in the sense that it would be exempt from having "antilock" and spring brakes as outlined in S5.8 of standard 121? Or is it to be classed so that it will require anti-lock and spring brakes? Your expeditious answer as to interpretation is appreciated.

Sincerely, Al Zajic -- Project Engineer, AMERICAN TRAILERS, INC.

Encl:

(Graphics omitted)

LEAD TRAILER

SECOND TRAILER

PERMANENT 360 DEGREES TURNTABLE

ID: nht74-2.21

DATE: 08/12/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: B. F. Goodrich Aerospace and Defense Products

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your June 4 and June 20, 1974, letters asking if a parking brake system which locks mechanically after the brake is applied by any emergency air supply acting through the service air brake chamber would comply with Standard No. 121, Air brake systems. The parking brake provisions require in part:

S5.6.3 Application and holding. The parking brake shall be applied by an energy source that is not affected by loss of air pressure or brake fluid pressure in the service brake system. Once applied, the parking brakes shall be held in the applied position solely by mechanical means.

The arrangement described would not meet this requirement because the energy source to apply the brakes (the emergency air supply) would be affected by loss of air pressure in the service brake system. For example, any failure in the service brake piston diaphragm would cause a loss of air pressure that would in turn "affect" the energy source that applies the parking brakes. The brake chamber housing assembly is an element which is not considered to be part of the service brake system for this requirement.

I would like to point out that the provisions of Standard No. 121 do not apply to trailers manufactured before January 1, 1975.

Your truly,

ATTACH.

June 4, 1974

CHIEF COUNCIL -- U. S. Department of Transportation National Highway Traffic Safety Administration

Dear Sirs:

The following inquiry is submitted to you with regards to telephone conversations with Mr. S. F. Williams on Friday afternoon, May 31, 1974, and Monday morning June 3, 1974.

Will MVSS 121 permit actuation of a mechanically locking parking and/or emergency brake, using air that is applied to the service brake diaphragm?

The air is supplied, of course, from an isolated emergency source.

Yours truly, B. F. GOODRICH ENGINEERED SYSTEMS COMPANY A Division of The B. F. Goodrich Company;

A. J. Burt -- Sales Engineer

CC: S. F. Williams, D.O.T.; R. D. Buehler, B. F. Goodrich, Washington D. C.; C. R. Collins, B. F. Goodrich, Springfield, Virginia

B. F. Goodrich Aerospace and Defense Products

June 20, 1974

S. F. WILLIAMS -- U. S. Department of Transportation, National Highway Traffic Safety Administration

Dear Sid:

Relative to our phone conversation this afternoon, attached is a copy of all the technical information we have concerning the Park-Lock brake.

The Park-Lock people that we talked to in February of this year were Mr. Joe D'Angelo and Mr. Paul Mantle.

I should note that my inquiry to the Chief Council dated June 4, 1974 and copied to you, is meant to be interpreted as a generalized question concerning the use of a service brake diaphragm. The "mechanically locking parking and/or emergency brake" was not meant to refer specifically to the "Park Lock" device, but any general device which would require actuation by emergency air applied to a service brake diaphragm, and then mechanically locking once the actuation stroke is completed.

Yours truly,

A. J. Burt -- Sales Engineer, Highway Products

CC: R. D. Buehler -- B. F. Goodrich, Washington, D.C.; C. R. Collins -- B. F. Goodrich, Springfield, Virginia

Park-Lock

(Illegible Word) PARK LOCK?

Park Lock is an Automatic Brake Holding Device that holds your brakes, once applied . . . A New Friend to the Trucks.

WHAT DOES PARK LOCK DO?

Park Lock prevents trailer roll offs; climinates wheel chocking; prevents release of brakes when service system air pressure is below safe operating level.

HOW IS PARK LOCK APPLIED?

In emergency conditions, such as loss of air, the Relay Emergency Valve applies your brakes. . . As the air leaks off, Park Lock gently applies, automatically, and holds your brakes by mechanical means.

HOW IS PARK LOCK RELEASED?

There are two ways to release Park Lock.

1. With the application of air, Park Lock releases automatically.

2. By mechanical means. No special wrench is required. Pliers, screw-driver or coin can be used.

IS PARK LOCK SAFE?

Park Lock is a true safety device. Any child can dismantle it without danger (no explosion hazard).

DOES PARK LOCK WORK ON EQUIPMENT PRESENTLY IN USE?

(Units in service prior to S-121 and September 1, 1974)

Park Lock can be installed on all trailers, new and used. The Relay Emergency Value and air tank, currently on all trailers, applies your brakes. Park Lock holds your brakes mechanically, thus preventing trailer roll-offs.

IS PARK LOCK DURABLE?

The Park Lock casting is made of especially treated aluminum, for long, tough wear. Park Lock has four movable parts that include a special brake rod. Park Lock is mounted on your present brake chamber and plumbed into the Relay Emergency Value. Installation is easy and simple. The Park Lock weighs about two pounds.

PARK LOCK AND S-121 (After September 1, 1974)

Park Lock passes all requirements under S-121, pertaining to both parking brakes and emergency brakes for your trailers. It is used in conjunction with a Relay Emergency Value and air tank (same tank used under S-121 to release the spring brake).

Park Lock works in conjunction with your New Anti-Skid Braking System and allows you to come to a complete anti-skid stop. This is accomplished by plumbing the air (emergency mode) back through the anti-skid computer valve.

Park Lock can be released from the tractor cab by the same method used to release the spring brake. As required by S-121, Park Lock has a manual release that can be released from the unit.

HOW DOES PARK LOCK SAVE YOU MONEY?

Park Lock eliminates trailer roll-off accidents. This will reduce insurance claims. . . thus reduce insurance premiums.

Park Lock virtually eliminates replacement costs. There are few moving parts.

The sole function of Park Lock is to hold your brakes, once applied; therefore there is virtually no wear on the units.

Park Lock requires very little maintenance, which eliminates down time.

Park Lock eliminates wheel-chocking and need for expensive chocks, chains, and locks.

Park Lock protects your landing gears. No more damage to the landing gear caused by hooking the tractor to the trailer, running fork lifts into the trailer while loading, etc.

(Illegible Words) FIND OUT MORE ABOUT PARK LOCK?

For more information about Park Lock write or call

PARK LOCK, INC. 8240 C Moberly Dallas, Texas 75272 (214) 381-2237

(Illegible Text)

(Graphics omitted)

INVENTORS

Woller Case William F. Benefield to and communicating with said first bore, the said brake actuating red having a series of rack teeth transversely thereof and operatively extending through said first bore and connected at one end to said power element and connected at its opposite end through a linkage to said brake crank and a spring biased pawl rod in said second bore and a salenoid coil connected into the electrical system of said vehicle and embracing said pawl rod whereby, which said salenoid coil is energized, the pawl rod is operated to (Illegible Word) the rack teeth on said brake actuating rod and restrain the same in position to set the brakes.

2. In a brake getting mechanism, as described in claim 1, the said spring actually biasing the pawl rod in retracted position to (Illegible Words) said pawl rod being extended to engage said brake actuating rod by said solenoid against the tension of said spring.

3. In a device as described in claim 1, and a collar on said pawl rod for adjusting the tension of said compression spring.

(Illegible Line)

UNITED STATES PATENTS

(Illegible Table)

GEORGE E. A. HALVOSA, Primary Examiner

UR Ct. XR 74-503; 192-3; 188-163

ID: nht74-2.22

DATE: 06/12/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Southern Railway System

TITLE: FMVSS INTERPRETATION

TEXT: In your letters of January 10, 1974, and May 17, 1974, you have asked if a trailer would comply with S5.8 of Standard No. 121, Air brake systems, ("have a parking brake system. . . when the air pressure in the supply line is at atmospheric pressure") if its parking brake system contained a valve that allows manual release of the parking brake with the supply line at atmospheric pressure but automatically resets itself when the supply line is pressurized, so that the parking brake system operates as specified by S5.8. Such a valve would permit limited motion of trailers on flat cars to cushion shock experienced during transit.

Such a valve does not appear to conflict with the intent of S5.8 that the parking brake system apply when the supply line is at atmospheric pressure. The requirement is not intended to interfere with intentional manual release of the parking brakes after automatic application has occurred. The danger of inadvertent disablement of the parking brake system during subsequent highway travel is avoided by the automatic features which would return the system to normal operation as soon as the trailer is connected to a source of air pressure, i.e., a tractor.

Sincerely,

ATTACH.

May 17, 1974

Richard B. Dyson -- Assistant Chief Counsel for Regulations, National Highway Traffic Safety Administration, U. S. Department of Transportation

Dear Mr. Dyson:

Please refer to my letter dated January 10, 1974, and I also refer to my telephone conversations of May 17 and earlier with Mr. (Illegible Word) of your office, concerning the problems created for trailers to be used on railroad flat cars by the new requirements for parking brakes.

Attached is a memorandum dated May 17, 1974 from Southern Railway's Assistant Vice President - Engineering & Research C. E. Webb, explaining why there is a need for a parking brake system on a trailer which will allow it to move longitudinally along a flat car for a short distance during impact. Read literally, Section S5.8 of the new regulations would require a trailer to be equipped with a parking brake designed so that the trailer would be incapable of this short longitudinal movement on impact. Mr. Webb in his memorandum proposes parameters for a device, to be developed by the manufacturers and approved by DOT if necessary, which would achieve the purpose of the new regulation when the trailer was in over-the-road use, while at the same time meeting the need for a means to "cut out" the parking brake when the trailer is on a rail car. Mr.

Webb envisions a fail-safe device. I might add that by proposing the device described by Mr. Webb, Southern intends to take no exception to a change in the rules which would be more liberal, that is, allow devices to be put on trailers that would also allow the manual disabling of the parking brake in other situations where it may be desirable, e.g., in freight yards during hostling.

As I said in my January 10 letter, we believe @ 5.8 does not forbid installation of a device like that described by Mr. Webb. However, in order to interest manufacturers in developing the device, we feel it important that your agency indicate that it would be proper and permissible under your regulations. Therefore, we would appreciate receiving advice from you to that effect, if that is the view of your agency.

Thank you.

Yours sincerely,

William P. Stallsmith, Jr. Senior General Attorney -- SOUTHERN RAILWAY SYSTEM

ID: nht74-2.23

DATE: 09/24/74

FROM: AUTHOR UNAVAILABLE; James B Grefory; NHTSA

TO: Midland-Ross Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Midland-Ross' February 8, 1974, petition for an amendment of S5.1.2.1 and S5.2.1.2 of Standard No. 121, Air brake systems, to establish separate air reservoir volume requirements for several brake chamber types generally available in the air brake component market.

The standard presently requires air reservoir volumes to be a multiple of the vehicle's brake chamber volumes. Midland-Ross also requested that S5.1.2.2 and S5.2.1.3 be amended to require that a reservoir withstand hydrostatic pressure five times greater than stated on its label without rupture, or permanent circumferential deformation exceeding one percent. The standard presently requires that an air reservoir withstand internal hydrostatic pressure of five times the vehicle compressor cutout pressure or 500 pounds, whichever is greater. The pecition also requests modifications of the trailer test rig, which were made in a recent amendment of the standard (39 FR 17563, May 17, 1974).

You suggested that our requirement for air reservoir volume as a multiple of brake chamber volume will encourage installation of smaller equipment and thereby create a safety problem. We cannot agree, in view of the standard's stopping distance requirements which in effect mandate the installation of high performance components. Indications to date are that manufacturers have in fact not reduced brake chamber volumes. A certain degree of chamber stroke standardization may occur, which the NHTSA views as favorable. For these reasons your request is denied.

With regard to the air reservoir pressure requirements of S5.1.2.2 and S5.2.1.3, you argued that a reservoir manufacturer is unable to establish the required strength of his product because he cannot control the compressor cutout pressure of the vehicle on which the reservoir is installed. It should be understood that the standard is not an equipment standard with which Midland-Ross must comply, but a vehicle standard with which the vehicle manufacturer must comply. We have determined that the reservoir should be designed to manage the pressures to which it might be exposed on the vehicle on which it is installed. The vehicle manufacturer is able to establish a compressor cutout pressure (on powered vehicles, and, based on that value, order the appropriate reservoir to meet the requirement. It is evident that commercial considerations will standard compressor cutout pressures on reasonable range of available reservoir strengths. Midland-Ross as a manufacturer of reservoirs is free to establish a range of reservoir strenghts, and label the reservoirs as described in your petition. For the reasons cited, however, your petition to mandate this is denied.

We agree the requirement that a reservoir "withstand" a certain pressure can be further specified, and we are considering a proposal to do this in the future.

At this time the NHTSA has adopted the SAE Standard No. J10a, which specifies that there be no rupture or permanent circumferential deformation exceeding one percent.

Sincerely,

ATTACH.

PETITION FOR RECONSIDERATION

FEDERAL MOTOR VEHICLE SAFETY STANDARD 121 DOCKET 73-13 NOTICE #3

BY POWER CONTROLS DIVISION MIDLAND-ROSS CORPORATION

M. J. Denholm Director of Engineering

February 8, 1974

Midland-Ross regrets to find that several of the proposals issued under Notice 1 of Docket 73-13 have not been incorporated in the rule issued under Notice 3 of the Docket.

The purpose of this petition is to request reconsideration of outstanding petitions and comments not yet resolved or acted upon from previous notices. In addition, we wish to offer additional information to supplement our comments on Docket 70-16 and 17, Notice 3, and the petition for reconsideration of Docket 70-17, Notice 4.

Taking the sections as they appear in FMVSS 121 as amended by Docket 73-13, Notice 3, we ask for your consideration of the following:

S5.1.2.1

S5.2.1.2

On March 23, 1972, we petitioned for consideration of this section of Docket 70-16 and 70-17, Notice 3.

Quote: "The combined volume of all service brake chambers at maximum travel of the pistons or diaphragms" requires definition in that volume can be measured in more than one way resulting in significant variation in result. For example: Displacement determined by pressurizing a chamber hydrostatically to 5 psig would result in approximately 10% less volume as compared to that indicated when the same chamber is pressurized to 100 psig hydrostatically. The hydrostatic pressure would be applied using an incompressable fluid; the volume of fluid displaced being the measure of the chamber volume. We recommend the standard be revised to read as follows:

'S5.1.2.1 . . .the combined volume of all service brake chambers at maximum travel of the pistons or diaphragms when measured with 5 psig applied to the chamber.' This will eliminate the possibility of a dual standard when determining compliance."

On August 14, 1973, we petitioned again for reconsideration of this section of Docket 70-17, Notice 4; and again on July 11, 1973, against Docket 73-13, Notice 1.

Quote: "The requirement under both these sections is restrictive and not necessarily in the public interest. For example, Midland-Ross Type 30 service chambers provide 2.75 inch stroke where units of other manufacturers are as low as 2.5 inch. The long stroke provides a desirable margin for poor brake adjustment. We believe this advantage will render our product non-competitive. To become competitive a reduction in stroke, with the attendant reduction in reservoir capacity requirement will be necessary. We feel, in light of recent experience with designs to meet FMVSS, 121, Notice 4, that this is arbitrary and an unnecessarily expensive retrograde step, caused by the wording of this section. In addition, chamber displacement varies dependent upon the applied pressure.

"This is caused by ballooning of diaphragms as pressure is increased. It should be noted that a three or four axle rigid truck would require significantly larger reservoirs under this rule than would a two-axle tractor designed to tow two or three trailers. Taking into account these three factors, it is recommended that S5.1.2.1 and S5.2.1.2 be reworded as follows:

'S5.1.2.1 The combined volume of all service reservoirs and supply reservoirs shall be at least the value obtained by the following product: Buses, and tractors and trailers designed to tow air-braked vehicles:

(12) x (115%) x (Combined volume of all service brake chambers)

Trucks not designed to tow other air-braked vehicles: (8) x (115%) x (Combined volume of all service brake chambers)

The combined volume of all service brake chambers is that volume obtained at maximum travel of the pistons or diaphragms with 100 psi hydrostatic pressure applied to the chambers with the brakes adjusted as specified by the vehicle manufacturer for new, unburnished brakes.

'S5.2.1.2 The total service reservoir volume shall be at least the value obtained by the following product: (8) x (115%) x (Combined volume of all service brake chambers)

The combined volume of all service brake chambers is that volume obtained at maximum travel of the pistons or diaphragms with 100 psi hydrostatic pressure applied to the chambers with the brakes adjusted as specified by the vehicle manufacturer for new, unburnished brakes."

No action has resulted from any of these petitions. We feel both arguments are still valid. We would like to add additional argument to that furnished on August 14, 1973, as follows:

An optional method of determining reservoir volume would consist of using an established minimum working volume for each standard size of service chamber. The minimum working volume would then be used to compute the reservoir requirement in the manner stated in the standard. Using this approach, the need for the changes recommended on March 23, 1972, would be eliminated also. We therefore recommend the S5.1.2.1 be reworded as follows: S5.1.2.1 The combined volume of all service reservoirs and supply reservoirs shall be determined by adding the volumes specified in Table V, Column 1 for each air-operated service brake actuator.

S.5.2.1.2 shall read:

S5.2.1.2 Total service reservoir volume shall be determined by adding the volumes specified in Table V, Column 2 for each air operated service brake actuator.

TABLE V Reservoir Volume Required Per Actuator * Column 1 * Column 2 Actuator Trucks-Buses Trailers Type 9 Diaphragm 240 cubic inches 160 cubic inches Type 12 Diaphragm 300 cubic inches 200 cubic inches Type 16 Diaphragm 528 cubic inches 352 cubic inches Type 20 Diaphragm 612 cubic inches 408 cubic inches Type 24 Diaphragm 732 cubic inches 488 cubic inches Type 30 Diaphragm 1056 cubic inches 704 cubic inches Type 36 Diaphragm 1464 cubic inches 976 cubic inches

*Piston or Rolling 12 x volume at max. 8 x volume at max.

Diaphragm working stroke working stroke

The above revisions to S5.1.2.1 and S5.2.1.2 are requested due to the variation in design of diaphragm type service brake chambers. These chambers are of generally similar construction, but because of manufacturing tolerances and slight differences in stroke length, their maximum volumes are different by a few percentage points. The current reservoir volume requirement based on maximum displacement encourages the use of small volume chambers (to reduce required reservoir volumes). In use, however, these small volume chambers provide less reserve than larger displacement units. This is true because the larger displacement units generally have slightly longer operating strokes. This additional stroke is a safety advantage in event that brake drums expand from heat buildup or shoes are allowed to wear without brake readjustment.

The chamber volume differences caused by variations in maximum stroke length are not significant to a vehicle in normal operation. This is because either chamber design would require the same amount of air to operate a properly adjusted brake; either unit when stroked to the same distance (any value short of maximum stroke; would displace nearly the same volume of air. Chamber volume requirements per brake application would be the same for either chamber design unless the stroke exceeded the maximum stroke length of the short stroke chamber. In that case, (abnormal situation) the long stroke chamber would require more air than a short stroke unit but would produce brake torque to stop the vehicle. The short stroke unit would be stopped internally without producing brake torque.

If S5.1.2.1 and S5.2.1.2 are not revised, market pressure will force redesign of long stroke chambers to limit stroke (and maximum volume). This could be carried to an extreme whereby the redesigned chambers would have even shorter strokes than current chambers. This type unit would then have economic advantages that would encourage their use; but they would actually be inferior to current chambers from a safety point of view.

The chamber volumes proposed in Table V were arrived at by applying the current requirement of 12 times chamber volume at maximum stroke (eight times for trailers) to the maximum volume of the truck industry's most common air brake chamber. These values do not represent a change in the spirit of the law, only in its detail. The original method of determining reservoir volume would be retained for piston actuators or other devices whose stroke and displacement have not become standardized in the industry.

S5.1.2.2

S5.2.1.3

On March 23, 1972, we petitioned for reconsideration of both of these sections of Docket 70-16 and 70-17, Notice 3.

Quote: "The requirement that the reservoirs under both of these sections should 'withstand' an internal hydrostatic pressure is nondefinitive and open to interpretation. In addition, manufacturers of air brake reservoirs are not necessarily in a position to determine what the cutout pressure of the compressor will be for a particular reservoir application prior to design and development of the reservoir as required under Paragraph S5.1.2.2. In addition, there is a significant inconsistency between the requirements for reservoir strength on a truck or bus and those for reservoirs used on a trailer as both reservoirs on a combination vehicle would be pressurized by the same compressor to the same pressure levels. It would appear reasonable, in the interest of safety, to adopt a common standard. It would also appear to be advisable to use a standard which is both proven and perfectly acceptable based on long periods of experience. It is therefore recommended that Paragraphs S5.1.2.2 and S5.2.1.3 be revised as follows:

'Each reservoir shall be capable of accepting a hydrostatic pressure of not less than five times the reservoir rated working pressure for a minimum of one minute. When subjected to this pressure for this time period there shall be no rupture or permanent circumferential deformation exceeding 1%. The reservoirs meeting this requirement must be permanently identified for rated working pressure."

On August 14, 1973, we again petitioned for reconsideration of these sections of Docket 70-17, Notice 3. Comments were also made on Docket 73-13, Notice 1.

Quote: "The requirement that the reservoirs under both of these sections should withstand an internal hydrostatic pressure is nondefinitive and open to interpretation. In addition manufacturers of air brake reservoirs are not necessarily in a position to determine what the cutout pressure of the compressor will be for a particular reservoir application prior to design and development of the reservoir as required under Paragraph S5.1.2.2. In addition, there is a significant inconsistency between the requirements for reservoir strength on a truck or bus and those for reservoirs used on a trailer. Both reservoirs on a combination vehicle would be pressurized by the same compressor to essentially the same pressure levels. It would appear reasonable, in the interest of safety, to adopt a common standard. It would also appear to be advisable to use a standard which is both proven and perfectly acceptable based on long periods of experience. It is therefore recommended that Paragraphs S5.1.2.2 and S5.2.1.3 be revised as follows:

'Each reservoir shall be capable of accepting a hydrostatic pressure of not less than five times the reservoir rated working pressure for a minimum of one minute. When subjected to this pressure for this time period, there shall be no rupture or permanent circumferential deformation exceeding 1%. The reservoirs meeting this requirement must be permanently identified for rated working pressure.'

Note: This recommendation reflects the current SAE Standard Practice (SAE J10b) in regard to reservoir certification and therefore should provide clarification without creating unnecessary hardships."

An additional point which was not specifically made in the two petitions quoted from relates to manufacturing practice and product application.

As a major reservoir manufacturer, Midland-Ross produces all reservoirs for air-braked vehicles in one of three diameters. Each diameter is engineered from differing material thicknesses to withstand a predetermined working pressure. Usually this is 150 psi. When reservoirs are supplied to the industry we have no knowledge of the compressor cutout pressure. The compressor cutout pressure is usually adjustable in service. A situation over which the reservoir manufacturer has no control. By establishing a maximum rated working pressure for the reservoir to be marked on the unit, the user then has direct knowledge of the limit to which the compressor cutout pressure can be safely adjusted. We feel that adopting this method would result in better understanding on the part of the user as this has been the standard used historically. It would eliminate the need to re-educate operators and provide a sounder basis for economic reliable manufacture and application of air brake reservoirs.

S5.3.3

S5.3.4

On March 23, 1972 we pointed out in our petition for reconsideration the inadequacies of the test standard shown in Docket 70-16 and 70-16, Notice 3, Figure 1. Partial response to this petition was exhibited in Docket 73-13, Notice 1, S6.1.12.

Docket 73-13, Notice 3, essentially returns to 70-17, Notice 3 level, thus effectively ignoring our original petition and also our comments on Docket 73-13, Notice 1, submitted to the Administration on July 11, 1973.

We ask for consideration of our updated proposal as follows:

S5.3.3 Brake actuation time. With an initial service reservoir system air pressure of 100 psi, the air pressure in each brake chamber shall reach 60 psi in not more than 0.25 second measured from the first movement of the service brake control. A vehicle designed to tow a vehicle equipped with air brakes shall be capable of meeting the above actuation time requirement with a 50-cubic-inch test reservoir connected to the control line coupler. A trailer shall meet the above requirement with its brake system connected to a trailer timing test rig as shown in Fig. 1 which meets the requirements of S5.3.3.1 and S5.3.3.2.

S5.3.3.1 The following should be added:

"The trailer test rig shown in Fig. 1 shall be constructed such that the pressure in a 50 cubic inch test volume connected to the control coupling is raised from zero to 60 psi in .063 second minimum when tested on the test rig. Time shall be measured from the first mechanical movement of the device controlling air flow to the control coupling."

S5.3.3.2 The following should be added:

"The trailer test rig shown in Figure 1 shall be constructed such that the pressure in a 50 cubic inch test volume connected to the control coupling is exhausted from 95 to 5 psi in .220 second minimum when tested on the test rig. Time shall be measured from the first mechanical movement of the device controlling air flow from the control coupling.

Figure 1 should be revised as shown:

(Graphics omitted)

S5.3.4 Brake release time. With an initial brake chamber air pressure of 95 psi, the air pressure in each brake chamber shall fall to 5 psi in not more than 0.50 second measured from the first movement of the service brake control. A vehicle designed to tow another vehicle equipped with air brakes shall be capable of meeting the above release time requirement with a 50-cubic inch test reservoir connected to the control line coupling. A trailer shall meet the above release time requirement with its brake system connected to the test rig shown in Fig. 1 and which meets the requirements of S5.3.3.1 and S5.3.3.2.

The above changes to Section S5.3.3 and Figure 1, and additions to S5.3.3.1 and S5.3.3.2 are recommended in an effort to more completely define the TRAILER TEST RIG. Until this rig is defined, uniform timing will not exist on trailers built to FMVSS 121. The original Figure 1 was designed to duplicate a tractor. It did this but as a test instrument it is inadequately defined. The air delivery performance of this device (as well as the tractors it was modeled from) will vary significantly. This is unacceptable when proof of vehicle compliance to the standard depends upon tests made with this unit. The proposed Figure 1 is a black box with narrowly defined performance characteristics. Devices built to this requirement will undoubtedly exhibit performance variations when tested against one another, but their level of consistency will far exceed that obtained by a unit in the standard which is only partly defined.

ID: nht74-2.24

DATE: 07/03/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: White Motor Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your recent request for an interpretation of S5.3.1.2 of Standard No. 121, Air brake systems. That section permits certain vehicles to avoid the stopping distance requirement if their brakes conform to a retardation formula and values found in another section of the standard (S5.4.1).

The language of S5.3.1.2 makes clear that any truck in the described category need not meet the stopping distance requirements if its brakes satisfy the retardation formula and values of S5.4.1, and therefore none of the exceptions found in S5.4.1 apply to vehicles subject to the requirements of S5.3.1.2.

This interpretation also appears in the preamble to Notice 2 of Docket No. 73-10, and is enclosed for your information.

Yours truly,

ATTACH.

James B. Gregory, Administrator -- National Highway Traffic Safety Administration

Subject: Request for Interpretation of Standard 121, Docket 74-10; Notice 2, Section 5.3.1.2

Dear Dr. Gregory:

The amended standard, Section @ 5.3.1.2 states that a vehicle manufactured before September 1, 1975, that has a front steerable axle with a GAWR of 16,000 pounds or more, or a front steerable drive axle, need not meet the stopping distance requirement if its brakes conform to the retardation formula and values of @ 5.4.1 applied to the vehicle as a whole and to the front axle system separately.

However, Section @ 5.4.1 as now amended, applies only to "each vehicle designed to be towed by another vehicle equipped with air brakes" and, therefore, there are no retardation requirements applicable to either a towing vehicle or to a vehicle which is used by itself. Under the circumstances, it would appear that such vehicles would not be required to meet any specific retardation requirements.

We request an interpretation of the applicability of @ 5.4.1 to these special classes of vehicles for the interim period where no stopping distance requirements are in effect.

Sincerely, WHITE MOTOR CORPORATION; J. W. Lawrence -- Manager Safety and Environmental Engineering

ID: nht74-2.25

DATE: 05/10/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Kelsey-Hayes Company

TITLE: FMVSS INTERPRETATION

TEXT: This will acknowledge receipt of Kelsey-Hayes' petition to add "after-stop" to the description of temperature range in S6.1.8.1 of Standard No. 121 and S7.4.2.1.2 of Standard No. 105a.

The temperature range is in fact intended to describe the after stop temperature of the brakes, and the language of the sections will be clarified in the future.

Yours truly,

ATTACH.

April 25, 1974

U. S. Department of Transportation, National Highway Traffic Safety Administration,

Richard B. Dyson -- Assistant Chief Counsel

RE: Requests for Interpretation -- FMVSS 105 (9/1/75) S7.4.2.1.2; FMVSS 121 S6.1.8.1; Your file numbers N40-30 (ZTV) and (TWH); Brake Burnish Procedure

Dear Mr. Dyson:

You have responded to our requests for interpretation on identical language in these subsections of these standards and advised that the word maximum would be deleted in the sentence ending in ". . . maintain a maximum temperature of 500 degrees F +/- 50 degrees F."

We recommend one further clarification to eliminate ambiguity, namely, that the phrase "after-stop temperature" be added to the sentence, as follows:

"If during any of the brake applications specified in , the hottest brake reaches 500 degrees F, make the remainder of the 500 applications from that speed except that a higher or lower speed shall be used as necessary to maintain an after-stop temperature of 500 degrees F +/- 50 degrees F."

We further suggest that a notice be issued proposing this clarification.

Very truly yours,

John F. McCuen -- Attorney, KELSEY-HAYES COMPANY

cc: W. T. Birge; D. Renner

ID: nht74-2.26

DATE: 07/09/74

FROM: AUTHOR UNAVAILABLE; R. L. Carter; NHTSA

TO: Wanger Electric Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your March 12, 1974, request for interpretation of the volume requirements for service brake chambers in S5.1.2.1 and S5.2.1.2 of Standard No. 121, Air Brake Systems:

S5.1.2 Total service reservoir volume shall be at least eight times the combined volume of all service brake chambers at maximum travel of the pistons or diaphragms.

You also requested the addition of language equating brake chamber volume with brake chamber displacement, based on nominal effective area and rated stroke.

In testing for compliance with S5.1.2.1 and S5.2.1.2, the NHTSA will accept a manufacturer's published "rated volume" of the brake chamber with the piston or diaphragm at maximum travel. This means that the manufacturer may specify the full stroke of the piston or diaphragm and compute the "rated volume" based on the designed volume of the chamber and the full stroke he has established. This volume may be somewhat larger than "nominal brake chamber displacement" which does not necessarily account for the void ahead of the relaxed diaphragm or piston, the so-called "pre-fill volume". This volume must be included because it must be pressurized along with the displaced volume.

In the absence of manufacturer's published ratings, the NHTSA will measure the brake chamber volume with the push rod at maximum stroke.

Your request to add explanatory language to the standard of the measurement technique is denied as unnecessary in view of this interpretation.

Sincerely,

ATTACH.

March 12, 1974

James B. Gregory, Administrator -- National Highway Traffic Safety Administration

Re: Docket 73-13; Notice 3 74-10; Notice 1 49 CFR 571.121

Petition for Reconsideration FMVSS-121, Air Brake Systems

Dear Dr. Gregory:

We were pleased to note in the March 1, 1974, Federal Register (39FR-7966) that the NHTSA needed further consideration on petitions for air tank volume before an answer would be published.

We apparently did not place adequate emphasis on this facet of FMVSS-121 compliance. Instead of a petition, we addressed a letter dated July 13, 1973, to the Director, Office of Operating Systems, for an interpretation. In that letter we asked only one question and it is quoted below:

Will the NHTSA accept the vehicle or chamber manufacturers' nominal value for maximum allowable stroke on each actuator when determining the minimum vehicle reservoir capacity required by S5.1.2.1 and S5.2.1.2?

In view of the absence of any response to a fundamental question, the manufacturers of air-braked vehicles and air brake equipment have gone in divergent directions with their own "interpretations." Apparently, it is a more profound problem than we or our competitors anticipated. In defense of our commercial position in this product area, we now find it necessary to submit this letter as a Petition.

Petition (1) We petition for an answer to the question posed in our July 13, 1973, letter (as quoted above).

In support of this petition we have attached a copy of that letter as Appendix A. The unanswered question appears on Page 4.

We will risk being a little repetitious, but our concern is that too much emphasis is being placed on finite measurements of chamber volume and reservoir volumes. From a statistical viewpoint, the case of trailer reservoir volume is a classic example of compliance or certification "overkill." S5.2.1.2 reads:

S5.2.1.2 Total reservoir volume shall be at least eight times the combined volume of all service brake chambers at maximum travel of the pistons or diaphragms.

In mathematical terms the word "eight" has a numerical equivalent of 8. For degrees of accuracy it could be 8.0, 8.00, 8.000, --- but it was just commonplace old "number eight."

In our letter of July 13, 1973, we reproduced the SAE J813 Recommended Practice for Air Brake Reservoir Volume (see Page 2, Appendix A). A truck trailer was considered to need "not less than 4 times the actuator displacement volume at maximum travel of the piston or diaphragm." The industry has accepted this 100% improvement in stored volume. Now all we are trying to do is determine whether this gross volume can be determined by simple mathematics or will require ultra-sensitive physical measurement of the actuators and the associated reservoirs.

Not only do the simple calculations benefit the designers of vehicles and brake systems, they have an obvious benefit to the NHTSA Office of Standards Enforcement.

Does the Office of Operating Systems assign the accuracy of these measurements to four significant figures necessary to the safe operation of a trailer? We see no technical justification for this. If there is, then it should be public knowledge. This is our rationale. Again using the most popular trailer as the example: It has 2 cam brakes with type 30 (30 square inch nominal effective area) chambers for actuation. These chambers have a nominal stroke of 2 1/2 in. (one source has a 2 3/4 inch stroke).

Under SAE J813 the required reservoir volume is:

4 x (Nominal Area) x (Nominal Max. Stroke) x (No. of Chambers) = Volume or 4 (30) (2.5) (2) = 600 cubic inches.

Under S5.2.1.2 of FMVSS the simple approach is

8 (30) (2.5) (2) = 1200 cubic inches.

Now we industry specialists get concerned by public statements at NHTSA meetings that it should be easy to measure --- put it (chamber) on a table, stroke it under pressure and measure the volume.

Production tolerances may allow a maximum stroke to extend to 2.65 inches or another 8 (30) (0.15) (2) = 25 cubic inches.

A further study points out that chambers have a void ahead of the relaxed diaphragm. It is there to assure good entry of unrestricted air flow to the effective area. This pre-fill volume can be at least 5 cubic inches per chamber or (8) (5) (2) = 80 cubic inches per axle.

At full stroke the defection of the non-rigid diaphragm adds another approximate 12 cubic inches per chamber or 8 (12) (2) = 192 cubic inches per axle. It is not needed at mid-stroke. Therefore, this is a superfluous requirement. There are many other more significant factors affecting chamber/brake output if we consider brake effectiveness under such an extreme condition.

The gross addition for these three factors alone is -

25 cu. inches 80 cu. inches +192 cu. inches

297 cubic inches per axle.

Note 192 cubic inches is beyond the point of useful volume and should not be a part of this measurement anyway.

To prove compliance or non-compliance using all of the added factors would require a very sophisticated laboratory contract and allied equipment. The report would be documented by instrument calibrations and certifications traced back to the National Bureau of Standards.

Did the NHTSA really want its "doctrine of adversity" to become this costly a situation? We can't believe the task force responsible for the first issue of FMVSS-121 was that conversant with the detailed construction of chambers to recognize the disparity of viewpoints in measuring technique that have evolved. We are certain there was not one iota of data in the DOT contract files to substantiate this stringent a need. From the public meetings we recall that concern for reservoir size was subordinated in seriousness because trailers are thought to have all sorts of space for reservoirs. In some cases this is true. However, random tank placement is not possible. One other FMVSS-121 requirement makes remote tank locations impractical.

That requirement is the Brake Actuation Time found in S5.3.3. To reach 60 psi in 0.25 sec. from actuation of the test rig control requires optimum system designing --- this prohibits such luxuries as -

(a) long air lines to the chambers

(b) untested hose sizes for these line

(c) remote reservoirs to contain this superfluous volume of air.

We could not predict how essential all of this would be in 1971, but we have come a long way. It was late Spring, 1973, when we became extremely concerned about contract testing to evaluate reservoir volume. We had already acknowledged that we were part of a regulated industry. On July 13, 1973, we demonstrated our intent to act like we were being regulated and posed our "simple" question. We are disappointed that an early response was impossible to develop and furnish. We are further disappointed that the 1972 and 1973 petitions filed by a competitor on this same subject matter have not resulted in positive rulemaking actions to resolve the internal problems that must exist between the Office of Operating Systems and Office of Standards Enforcement.

Perhaps this aspect of FMVSS-121 is not as vital as decisions on the effective date, but rule content does influence ability to meet effective dates. We trust this reinforcement of open petitions will prompt immediate action.

In summary, we believe an affirmative reply to our July 13, 1973, question will not adversely affect vehicle safety. If there is any suspicion in the Office of Standards Enforcement that the vehicle manufacturers or chamber manufacturers would falsify their nominal stroke or nominal areas for these components to avoid "proper" sizing of reservoirs, then that should be a subject for docket comment. We are already charged with honest manufacturing recommendations for brake adjustment, air compressor capacity, interpretation of "controlled lockup," option choices for parking brake mode, transmission gear range, tire inflation pressure, gross vehicle weight rating, gross axle weight ratings, burnish options and others not mentioned.

Our conclusion is that the following petition will reflect a simple means for calculations:

Petition (2) We petition for the addition of this sentence to S5.2.1.2 (see Page 2): "For purposes of establishing reservoir volumes, brake chamber displacement is equal to the product of the nominal effective area and nominal rated stroke."

It may be that the relative ease of chamber and reservoir measurements makes them good "compliance targets," but if the enforcement of FMVSS-121 is reduced to such attack, the goal of the NHTSA and the efforts of the industry to attain these goals will be unjustly inhibited in future vehicle safety programs.

Very cordially yours,

WAGNER ELECTRIC CORPORATION; John W. Kourik -- Chief Engineer, Automotive Products

Attachment: Appendix A

WAGNER ELECTRIC CORPORATION WAGNER DIVISION

July 13, 1973

Elwood T. Driver, Code 41-30 -- Director, Office of Operating Systems, NHTSA

Gentlemen:

As a manufacturer of brakes and air brake actuating system components, Wagner Electric Corporation is desirous of consistent and accurate interpretations of all applicable Federal Motor Vehicle Safety Standards. We are encountering an increasing amount of confusion in the industry regarding the method or procedure to be used in establishing the air reservoir capacity for air brake vehicles as required by FMVSS-121 (Section 5.1.2.1 and Section 5.2.1.2). We are, therefore, requesting interpretation and/or clarification of these sections with regard to the wording ". . . the combined volume of all service brake chambers at maximum travel of the pistons or diaphragms . . ." as found in Sections 5.1.2.1 and 5.2.1.2.

While the method of measurement of brake actuator volume may seem insignificant, in some cases it has become a major concern to decide whether an existing reservoir volume can be used or whether a new air reservoir must be made up with a slightly larger capacity. The determining factor is how the brake actuator volume requirements are measured. Therefore, a prompt response would be most appreciated so that the design and specification of air system components required to meet FMVSS-121 can be finalized.

Prior to Docket 70-17 and Docket 70-16 work by the NHTSA the recommendation for air brake reservoir volume used by some of the vehicle manufacturers was SAE J813.

AIR BRAKE RESERVOIR VOLUME

AIR BRAKE RESERVOIR VOLUME -- SAE J813

SAE Recommended Practice

Report of Brake Committee approved November 1961

Scope -- This recommended practice establishes minimum volume requirements for air reservoirs for automotive vehicles using compressed air systems essentially for the actuation of the brake. Accessories that utilize compressed air for their operation are not included in the conventional air brake system and, therefore, additional volume must be provided for their requirements. Where air operated accessories are used, a check valve or equivalent device will be required to provide protection to the brake system.

These recommendations for minimum reservoir volumes in air brake systems are based on past experience and are intended as a guide in selecting the proper size reservoirs to assure an adequate source of braking power under normal level operating conditions.

General -- The volume of the brake actuators in the air brake system, commonly referred to as brake cylinders, brake chambers, or roto-chambers, varies with the diameter and travel of the piston or diaphragm. The reservoir volume depends upon the size and number of the actuators on the vehicle and the type of vehicle service. Recommended volumes are calculated in Table 1 by multiplying the total volume of all actuators by an experience factor. Depending on traffic conditions and terrain, reservoir volumes, greater than the minimum values, should be considered.

(Illegible Table)

This recommended practice had also been endorsed in the Final Report of the Consolidated Brake Task Force of the Joint AMA-TIMA Brake Committee dated October 28, 1965. SAE J813 was reproduced above to simplify the evaluation of the comments which follow for those individuals who were not acquainted with previous (and current) recommended practice. Note that trucks or truck-tractors required only eight (8) times the actuator displacement volume and truck-trailers only four (4) times the actuator volume. We know from our experience that the maximum travel used throughout the industry in determining actuator displacement was the nominal value for the stroke of the actuator and that there was no attempt to incorporate production variations due to manufacturing tolerances. When we compare the values for the volume in J813 with the requirements of S5.1.2.1 (trucks and buses) and S5.2.1.2 (trailers) it will be noted that significant improvement in the stored air volume has been made mandatory by FMVSS-121. There is even further significance in this change to the large volume requirement in that many vehicles were built and are being built in 1973 with reservoir capacities less than the requirements specified in J813.

Perhaps it was not recognized at the time that FMVSS-121 issued that the efficiency of brake chambers has the characteristic shown in Figure 2. The performance requirements of FMVSS-121 for (1) actual stopping distance measurements and (2) timing requirements are based on brakes being adjusted to the vehicle manufacturers' recommendation. Figure 2 demonstrates that the mid stroke of most brake chambers is the point of approximate 100% efficiency. Shorter strokes are associated with higher output than would be nominally expected. In S5.1.2.1 and S5.2.1.2 the volume of all service reservoirs and supply reservoirs is based on ". . . the combined volume of all service brake chambers at maximum travel of pistons or diaphragms." As vehicle manufacturers begin to finalize the design of the variety of systems essential to the different vehicle chassis, space for air reservoirs is precious. It is advantageous for the vehicle manufacturers and the component suppliers to select a limited number of reservoir sizes for the purposes of simplicity in design, ease of procurement, and economy of using a few standard reservoir sizes.

If the most adverse characteristics are to be determined for compliance, not only must the chambers be subjected to extremely close measurement of displacement but the net displacement of air reservoirs must be measured very precisely. We believe it is advantageous for the NHTSA to recognize that the twelve (12) and eight (8) times minimum volume requirement for trucks and trailers respectively does not require the same degree of accuracy needed to measure application and release times or to measure stopping distance compliance. We are therefore proposing that chamber strokes used in these calculations be based on the nominal values established as the maximum allowable stroke for the components installed on the vehicle. It will be noted in Figure 1 that the probable variation between a nominal stroke of 2.50" and a stroke which allows for all production tolerances is only 97.1-90.0 = 7.1 cubic inches per chamber. On a tandem axle trailer or a tandem drive axle tractor this 28 cubic inch variation has been noted to warrant an increase in the number of reservoirs essential for very precise compliance to the general requirement in Sections 5.1.2.1 and 5.2.1.2. This seems to be an unnecessary expense for the manufacturers to incur since standard reservoir volumes could be used at the lower value without any real sacrifice in vehicle performance. The slight variation in stored volume will not have any adverse effect on application time. If it did, then correction in the volume would have to be necessary in order to comply with the application time requirements for a given vehicle. We do not see that this slight volumetric difference is essential for skid control systems. It is characteristic of skid control systems to exhaust air from the service line and deplete the service reservoir(s). When skid control is functioning the performance of any system becomes self-limiting at a point at which the air pressure no longer produces sufficient brake torque to generate impending skids. Once this pressure level is achieved there is no further demand for reserve capacity in the air brake system. Therefore the stopping requirements for vehicles from 60 and 20 mph can be satisfied in the road test phase of FMVSS-121 without having to be too precise in establishing the actual net chamber/reservoir measurements.

Typical of some of the problems which can be generated by the preciseness of FMVSS-121 is the Figure 1 test rig for trailers. While 2000 cubic inch reservoirs could be obtained or could be made by modification of standard reservoir sizes, the typical unit produced in the industry is 2020 cubic inches. By using inert ballast material, a reduction of 20 cubic inches in the stored capacity of the reservoir is relatively easy. This is a case where we do not feel that a 20 cubic inch variation is really a significant part of the over-all performance requirement of either the vehicle or the test rig but the strict implementation of Figure 1 requires special equipment and added expense.

We have presented this appraisal of the situation which confronts the vendor and vehicle industry in order to provide some relief that will be of mutual benefit to the public, the vehicle manufacturers, and the NHTSA by concentrating on the critical aspects of FMVSS-121. If each phase of the Standard is put into its proper perspective it will enable the NHTSA and the industry to begin implementation of good cost/benefit practices. For this reason (Illegible Word) then ask the following:

Will the NHTSA accept the vehicle or chamber manufacturers' nominal value for maximum allowable stroke on each actuator when determining the minimum vehicle reservoir capacity required by S5.1.2.1 and S5.2.1.2?

For minor clarification, this question is directed at using (1) the middle of the three curves shown on Figure 1; (volume versus stroke at 100 psi) and (2) a volumetric requirement of 90 cubic inches at a nominal stroke of 2.50". We have encircled that point for emphasis.

Very truly yours,

John W. Kourik -- Chief Engineer, Automotive Products

Attach. Figures 1 & 2 (Graphics omitted)

ID: nht74-2.27

DATE: 06/12/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Truck Trailer Manufacturers Association

TITLE: FMVSS INTERPRETATION

TEXT: This is in response to your letter of May 29, 1974, concerning paragraph S5.3.2 of Federal Motor Vehicle Safety Standard No. 121, Air brake systems.

When a full trailer is tested for compliance with S5.3.2, the wheels on the steerable axle(s) cannot lock up at speeds above 10 mph except for controlled lockup of wheels allowed by an antilock system.

Yours truly,

ATTACH.

Truck Trailer Manufacturers Association

May 29, 1974

Larry Schneider -- Chief Counsel, National Highway Traffic Safety Administration

Subject: FMVSS-121 - Request for Interpretation

Dear Mr. Schneider:

A number of our members are currently involved in the redesign of braking systems in order to comply with the regulations specified by FMVSS.121. In this regard, we would appreciate your advice on the following:

Section S5.3.2 specifies antiwheel lockup control on all wheels except "lockup of wheels on non-steerable axles other than the two rearmost non-liftable, non-steerable axles on a trailer with more than two non-steerable axles."

Does this imply that all steerable axles must have antilock control?

Sincerely yours,

Burt Weller -- Engineering Manager